Hydraulic power transmission



'March 4, 1947. J, ROB|NV5ON HYDRAULIC POWER TRANSMISSION Filed July l, 1942 l1 lll llllllllll/l/l/l/l/l ll Il lll/ lll/ll ll /l ll l l /l/ lll/1A ATTORNEY Patented'Main 4, 1947l Y I UNITED N sTATizs lPATENT ,oF-FICE HYDRAULIC POWER TRANSMISSION James Robinson, Detroit, Mich., assignor to Vickers' Incorporated, Detroit, Mich., a corporation of Michigan Application July 1, 1942, Serial No. 449,213 v 4 Claims. ',(Cl. 60-53) This invention relates to power transmissions. A valve spool 40 is slidably mounted in bore 28 particularly to those of the type comprising two to selectively connect the pressure port to either or more fluid pressure energy translating devices, cylinder port and the other cylinder port to a one of which may function as a pump and an- 1 tank port. Valve spool 4I) comprises a stem havother as afiuid motor. 5 ing three lands thereon, 42, 44 and 46, which are It is concerned particularly with such a system provided with a plurality of holes extending rawhich has a variable displacement pump as the dially from bore 48.`l The lands 42, 44 and 46 pressure supply and especially with the means for of valve spool 40 are of a width suillcient to regulating the delivery of such pump. block their respective ports before opening the It has heretofore been customary when using same as the spool 40 is shifted, that is, when a pressure controlled variable displacement pump spool 40 is moved one-half'the effective operatin systems of this class' to use both open-center ing distance, in either direction, the lands thereand closed center directioneu control valves deof will completely obturate their respective ports pending on whether the operation of the pump so as to cause pressure in conduit 20 to build 11D was desired either at full stroke against neglifor a purpose hereinafter disclosed. The Spool 40 gible pressure or at minimum stroke against full is manually operated by lever 43 and is frictionelly pressure. In some cases it is desired to operate maintained in its three effective Operating posithe pump at negligible pressure and at minimum tions by a spring-pressed detent 50.

strokewhen the control valve is in central posi- The ttink Ports 32 and 34 of valve 25 connect tion, but this has not been possible with systems by conduits 52 and 54 to the tank, While the oylheretofore used, inder ports 36 and 38 connect by conduits 56 It is an Object of the invention therefore, to and 58 to either side of a iiuid motor unit generalprovide an improved power transmission system ly designated 60. The latter drives a load device wherein the pump may be operated bot-n at miniindicated by a hoist drum 62 on which a cable 64 mum displacement .and at minimum pressure may be wound or unwound to raise or lower a load when the motor is at rest. indicated diagrammaticauy at s6. For the pur- Further objects and iuvunurges` of the present pose of stopping the letter at any height there is invention will be apparent from the following de- Provided en automatic Pressure-released brake scription, reference being had to the accompany- Structure Which consists of supported `DiVoted ing drawing wherein a preferred form of the presarms 53 and 'ilwhch a're normally forced against s ent invention 1s (nearly shown a brake drum 12 bysprlngs 14 and 18, respective- In the drawing: ly, so that normally the arms 68 and 10 grasp and Figure 1 is a. diagrammatic view of a hydraulic hold the brake drum 12 mechanically. A cylinder power transmission System incorporating a pres- 80 is positioned intermediate the arms 68 and 10 sure compensating mechanism showing the lata'nd contains cppcsitciy acting Pistons Which ter in cross section and in one form .of the present When Pressure is admitted t0 the cylinder 80 Will invention be forced outwardly to release the hold on the Figure 2 is a side View of a portion of Figure 1. brake drum 12. Cylinder S ln Comunication In the embodiment of the invention shown 1n with the. pressure portee through e conduit a2. the drawing, a, motor m is adapted to drive e, The mechanism thus far described is wellvariable delivery pump l2 whose pistons are conknown equipment ancillary to the pressure regutained 1n a, yoke M The vohnne output of the lator hereinafter disclosed and per se forms no pump I2 is determined by the angular setting of Dart of the Present inventiollthe yoke I4 which in this cese is oscinatebleto The variable displacement Pump l2 is provided the leit away from vertical position in which the with a conduit 84 which connects the pressure displacement is zero, side thereof with a port 86 of a pressure regulating Pump l2 isprovided with a suction conduit I6 mechanism generally designated 88. The yoke I4 for. w1thdraw1ng fluid from a sump I8 and a of Dump I2 is connected by a link 90 to a rod or delivery condult 20. The latter -is provided with stem 02 of a piston 94. The latter is slidably a relief valve 22 for bypassing oil t0 the tank 50 mounted in a, cylinder 96 which is formed in a through a conduit 24 whenever a predetermined block 98 adapted to be mounted by means of a maximum pressure is exceeded in the conduit 20. mounting flange Surface |00 0n o suitable casing Conduit 20 extends to the pressure port of a |02 carried by the pump I2. 'I'he rod 92 of piston reversing valve 26 which, when in neutral posi- 94 is provided on its left end with a recess |04 tion, 1llustrated, bypasses the pump delivery to 55 for a purpose hereinafter disclosed.

the tank. The valve 26 comprises a main body A spring |06 normally biases the piston 94'to having a longitudinal bore 28 provided with anthe left, resting against an adjustable spring stop nular ports at spaced positions along its length |08 carried in the right hand end of the t e linder of which 30is a pressure port, 32 and 34 are tank A 96. Asuitable adjusting screw I I0 is provided in -ports and 36 and 38 are cylinder or motor ports. 60 the end wall of the cylinder 86 for adjusting the 3 spring stop |08 which is also used for limiting thestroke of the piston 94, and, although it does at the same time adjust the degree of compression of the spring |06, this adjustment of the spring does not affect the action of thev regulator as will be hereafter explained.

'I'he righthand end of cylinder 96 is connected with the tank by means of a passage I |2 communicating with a passage ||4 which extends from the interior of cylinder 96 to the exteriorof block 98. The passage I4 is adapted to be cut ol by the piston 94 as it approaches its righthand limit of movement, and thereafter all the oil discharged from the righthand end of the cylinder 96 must pass through an adjustable restriction orifice ||6l which is placed between the extreme righthand end of cylinder 96 and the passage ||2, thus effecting a dashpot action.

The'lefthand end of block 98 is provided with an end cover ||8 which closely envelops the rod 92 o1' piston 94 and contains a piston lock plunger or latch'l20. The latter is normally biased upward by a spring |22 and is adapted to become engaged in slot |04 and to hold the piston 94 retracted under conditions hereinafter,

disclosed. The lower end of cover ||8 is provided with a cap ||9 which contains a vent passage 2| serving to drain therethrough whatever fluid that may leak past the latch |20. The latter is connected to a pressure source for ac'- tuation thereof by a conduit |23 which communicates with the pressure conduit 84 through a chamber |32.

The extreme lefthand end of cylinder 96 communicates through conduit |24 with an overow chamber |26 of a balanced relief valve generally designated |28. The latter comprises a piston |30 slidable in the cylinder |32 and having a restricted orice |34 extending through the piston 30 and a central bore |35. A light spring |36 normally biases the piston |30 to the left. causing 1 the hollow stem thereof to seat on an annular seat |38 to close communication between passages 84 and |24. The control chamber |40 and the overflow chamber |26 of relief valve |28 communicate through passages |4| and |4-4, respectively, with a chamber |50 containing a pressure responsive pilot valve |42. Passage |44 communicates with the tank byv means of a restricted orice |46.

The .pilot valve |42 comprises a control valve sleeve |48 firmly mounted in the chamber |50 and having reduced diameterportions opposite the pasages |44 and |4| and permitting passage |44 to communicate with the interior thereof through a portl |I, while passage |4| is in coml munication .with the lower end, and thus constitutes the pilot pressure source. A control valve |52 is slidable in sleeve |48 and is yieldably maintained against its seat |49 under pressure of a light spring |54, the setting of which is controlled by an adjusting screw |56.

Control valve |52 consists of a cylindrical l'body.

having on its upper end a flange of somewhat larger diameter for seating purposes and a pair of oppositely extending holes in axial alignment,

which holes communicate through radially extending holes With its periphery, which at this point is of somewhat reduced diameter.` Pilot valve |42 when in thelowered position, illusvtrated, connects passage |44 with the tank.

through port 5| and the upwardly extending hole of control valve 52 and through passage |58. When lifted, pilot valve |42 connects the passage |4| with passage |44 through the downwardly extending hole of control valve 52 and thus vents chamber |40. Between its lowered -and lifted positions there is a mid position in The pressure required to maintain these conditions will be suilicient to hold the valve spool of control valve |42 in a partially raised position where ports |5| are cut off and passage |44 is consequently blocked at its vright-hand end, 'I'his pressure is transmitted undiminished through passages 86, |34 and |4| directly to valve |-42 because there is no flow through these passages to cause any drop in pressure. These passages, then, carry full line pressure. There is alower pressure maintained in the passages which communicate with chamber |26, and this pressure is dependent on the drop in pressure across seat |38 which in turn depends upon the position of pistonv |30 as well as the rate of flow across seat |38. Under stable conditions, the pressure maintained in chamber |26 must exactly balance the pressure created by spring |06 acting on the annular area of piston 94. |I 'his pressure is maintained by the action ,of valve 30 which, in order to achieve stability, must nd the proper -degree of opening which will pass the correct quantity of oil to supply the quantity escaping to tank through the ilxed orifice |46.

When the .pressure in delivery lines 20 and 84 tends to rise, the pressure will be felt through passage |34, chamber |40 and passage |4| so that control valve |42 will rise further to connect the controlchamber |40 with the overow chamber |26 through passage |44. This momentarily unbalances piston |30 permitting it to move slightly to the rightuntil it becomes balanced in a slightly more open position. As

this occurs, piston 94 will at first move to the right and, when it has brought the delivery- ,exactly balance the force of spring |06 in its more compressed condition.

Thus, anytendency for pressure to increase in lines 20-84 rst raises pilot valve y|42 to vent chamber |40. This permits valve 30 to open slightly wider andincrease the rate of flow across seat |38. Momentarily there is then more oil flowing into cylinder 96.through seat |38 than flows out through restrictor |46 so piston 94 must move to the right, reducing pump delivery and offsetting the tendency for pressure to rise in lines. 2li- 84. Also the oil` vented from chamber |40 is added to that already going into chamber 26 through seat |38, thus increasing the speed of rightward movement of piston 94.

When the linepressure' has thus fallen toy norn to tank through restrictor 46. There will be a higher pressure drop through restrictor |46, however, due to the necessity of maintaining in a,41e,so1

cylinder 96 a higher pressure to balance the increased force oi spring |06.

are the only possible pathsV of escape for the pump delivery, the pressure in line 20-84 will However, these variations in force exerted by spring |06 of piston 94 under varying degrees 'of compression have no effect on the delivery pressure on the pump. The only change in pump pressure which mayfbe present, at least theoretically, is that due tothe varying compression of the relief valve spring |36. However, this change is extremely minute and in actual practice may be neglected. The factor which controls relief valve |28 is the setting of the spring |54 of the pilot three-way valve |42. As the latter is subjected only to tank pressure on its upper end, it will be seen thatincreases in pressure in the lefthand end of cylinder 96 due to increased compression of spring |06 cannot produce corresponding increases in pressure in conduit 84.

Should the pressure in lines 20- 84 tend to fall off, valve |30 will remain stationary momentarily and valve |42 will move downwardly. This will connect passage |44 to tank through port and passages |52 and |58. Consequently piston 94 will move to the` left, exhausting fluid through passages |24, |26 and- |35. During this time the continuous ow through seat |38, passages |35 and |4| and restrictor |46 is maintained at a somewhat diminished value depending on how far the pressure has fallen off in line 84. When the piston 94 and yoke |4 have moved far enough to offset the falling off of line pressure, pilot valve I 42 will rise to its mid position, closing passage |44 and bringing the regulatorto a stable condition. Valve |30 will iind a new position slightly closer to seat |38 ythan before because slightly less oil is required to pass through seat |38 and out through passages and |44 and restrictor |46 due to the decreased compression of spring |06.

In operation, while the electric motor is being energized, pump |2, with the yoke I4 in the position illustrated, will deliver uid at a slow rate through conduit 20 to the reverse valve 26. T he latter, being in neutral position, illustrated, will bypass the liquid to the tank through bore 48 of valve spool 40, ports 32 and 34 and conduit 52. Under this condition fluid circulates through this path at substantially no pressure. As a result, the load device 66 is held stationary.

Should the need arise tov drive the load device 66 in the direction tending to lift it, lever 48 of valve 26 is pushed inward connecting pressure port 30 with cylinder port 36 and cylinder port 38 with tank port 34.i As spool 40 is shifted, the ports are momentarily blocked soy that there is no escape for the liquid delivered by the pump to pressure port 30. Pressure builds up accordingly in conduits 84, 86 and |23 very suddenly and causes latch |20 to be pulled outagainst the force of spring |22. The spring |22 preferably is relatively light and permits the latchv to be retracted at a low pressure in conduits 20, 84 and |23, that is, one lowerv than the pressure required to release brakes 68-10. The sudden rise ofpressure also temporarily causes valves |42 and |30 to respond and let additional oil into cylinder 96 to force piston 94 to the' right momentarily and relieve the frictional force on latch |20. This action being momentary, the pressure is almost immediately reduced by the continued not fall below the value at which latch |20 is held retracted, and consequently the piston 94 is free to advance'to the left as far as necessary to. build up the system pressure to the setting of valve |42. 4

Pump |2 being no longer bypassed, pressure will be transmitted to the conduit 20 and branch conduit 82 which being connected to cylinder 80 will urge the pistons therein outwardly releasing the hold on the brake drum 12, thus allowing the motor unit 60 to rotate in the direction tending to lift the load 66. It will be seen that thek automatic brake structure will be caused to release in response to the application of the given driving effort since, as the resisting load is applied to the hoist 62, the pressure in conduit 20 will be exactly proportional to the magnitude of that load resistance. 1 l

To stop the load 66 at a desired height," valve 26 is shifted 'to the position shown. This will again bypass the pump l2, causing the pressurereleased brake structure to take hold. During the interval of the shifting, however, the pressure port 30`of valve.26 will become momentarily blocked as hereinbefore described, causing the pressure in conduit 2'0 to build up to a point beyond the working pressure. 'This pressure transmitted to pressure regulator 88 will cause piston 94 thereof to be moved to the extreme rig-ht in a manner already described. As the shifting of valve 26 is completed and pump |2 becomes bypassed, the pressure in conduits 20 and 84 willagain drop substantially to zero permitting latch |20 to shift upward and become engaged in the piston recess |04, holding piston 94 in the position illustrated. This action is insuredby the extra length of slot |04 which permits some leftward movement of piston 94 while latch |20 is moving upwardly. It is also inmovement of valve spool 40, and, since piston sured by the fact that leftward movement of piston 94 is retarded by the necessity of forcing oil out through restrictor |46 andy the restricted passageways of valve |52. The upward travel of latch |20, however, is substantially unimpeded because of the small displacement of its piston and the relatively open passage |23 leading directly to the main line 2li- 84.

It will be noted that upon starting the motor in operation the latch |20 is at the righthand -edg'e of slot |04. Thus, the sudden pressure surge can quickly shift latch |20 downwardly and can only with great difficulty overcome the much greater inertia of piston 94 and yoke |4. Consequently, the latch is fully retracted While the piston 94 is barely moved during the short interval'that port 30 is blocked. When port 30 is then connected to a motor line, for example, line 56, the delivery line .pressure `is reduced somewhat but not nearly to zero so that latch |20 is not moved upwardly by its relatively light spring. On the other hand, piston 94 may shift leftward under the urge of its spring |06, and, after a very slight movement, slot |04zwill pass the latch |20 and it can no longer be eiective.

In contrast to this action at starting, the action at stopping is just the Opposite so far .as 'latch |20 is concerned. Valve spool 40 being shifted to block port 30, the latch will be quickly retracted, and the piston 94 willA- be shifted right-v might be adopted, all coming within piston 94 is travelling-the length of slot |04. Thus, the latch, due to its much'lower inertia.

and due to the extra length of slot -|04 as well as atv starting, the pump delivery line pressure does not drop to zero after the valve port 30' is unblocked but is maintained above the pressure which permits latch to engage by theneces- 'sity of 'releasing the brake and driving the load.

At stopping, however, the pump delivery line pressure is dropped substantially to zero after port 30 is unblocked, thus permitting latch |20 to engage.

member normally biased toward the` position of .full pump delivery, a valve for reversing and bypassing the supply of iluidto the motor, and a pressure-released latch for detaining said regulator in reduced delivery'position when the pump is by-passed, said latch being released by deliveryl pressure when the valve is shifted to motor operating position whereby the motor may be To lower the load 66,1lever 48 of lthe reversing.v e valve 26 ispulled outward connecting the pressure port-with cylinder port 38 and cylinder port 36 with tank port 32. It will be readily seen that during the lowering operation the load 66 tends to drive the motor 60 in the lowering direction, which tendency is resisted and ,overcomeby the brake. Thus pressure will rise until the brake is released sufficiently to permit motor 00 to rotate in the lowering direction at that pressure.

'I'he pressure in the system will be transmitted through conduit 04 to the `pressure regulator 80, and thence through conduit |23 to the latch |20.

The latter Vwill be forced downward, releasing its hold on piston rod 92. v

Thus it will be seen that the pressure compensator will not only maintain aconstant pump pressure within the volumetric range of the pump but will also unload the pump at its minimum capacity by.means'of a piston lock plunger which prevents unloading the pump at full capacity,

and, as a consequence, jerking action is eliminated upon starting.

While the'action of the pressure regulator 80 has been described with 'particular ref erence to its action under various conditions tending to cause a change in main line pressure, it will be seen that, with a hoist motor and brake device as disclosed,.this action will ordinarily take place only at the beginning and end of a period of hoisting or lowering operation. Naturally the regulator must be set to maintain pressure sufficiently high to drive the heaviest load encountered and any lesser load will not impose enough pressure to even lift pilot valve |42 at all. Consequently, after the initial acceleration the piston 94 will be fully extended to the left, and valve |30 will seatl on seat |38. T he imposition of an, overload will, of course, bring the regulatorl into action. at any time and will normally completely stop the hoist. yThe regulator does, however. come into action as previously described each time the directional control valve 26 is' operated to either stop or start the hoist. In so doing, the piston 94, having a restricted speed of movement, provides an excellent control over acceleration and deceleration of the hoist.

While the form of embodiment of the inventionas herein disclosed constitutes a preferred form, it is to be understood that other forms the scope of the claims which follow. 1 1

What is claimed is as follows:

l. A fluid power transmission system comprising in combination a uid pump and a fluid motor, a pump delivery regulator responsive to delivery pressure to normally maintain such pressure 4substantially constant, said regulator including a accelerated by the action of said regulator in moving to full deliveryiposition.

2. A fluid powertraiismission systexfn'comprising in combination'a'. fluid pump and a luid motor, a pump delivery regulator responsive to delivery pressure to normally maintain such pressure substantially constant, said regulator including a member normally biased toward the position of full pump delivery, a valve for reversing and bypassing the supply of fluid to the motor, and a pressure-released latch for detaining said regulator in reduced delivery position when the pump is bypassed, said latch being released by.

delivery pressure when the valve is shifted to motor operating position whereby the motor may be accelerated by the action of said regulator inr moving to full delivery position, said valve having its ports arranged to be momentarily blocked duringv shifting between bypassing and motoroperating positions, whereby a pressure surge may be built up to operate said latch.

3. A fluid power transmission system comprising in combination a fluid pump and a `fluid motor, a pump delivery regulator responsive'to delivery-pressure to normally maintain such pressure substantially constant, said regulator includ-# ing a member normally biased toward the position of full pump delivery, a valve for reversing and bypassing the-supply of uid to the motor, and a spring-engaged, pressure-released latch for detaining said regulator in reduced delivery position when the pump is bypassed, said latch having less inertia than said regulator and being released by delivery pressure when the valve is shifted to motor operating position, whereby the motor may be accelerated by the action of said regulator in moving to fullv delivery position.y

4. A fluid power transmission system comprising in combination a fluid pump and a fluid motor,I a pump delivery regulator responsive to delivery pressure to normally maintain such pressure substantially constant, said regulator including a member normally biased toward the position of full pump delivery, an open-center,

four-way valve for reversing and bypassing the delivery position.

- JAMES ROBINSON.

REFERENCES CITED The following references are of record in'the le of this patent: f

' UNITED STATESl PATENTS 

